Double-ply corrugated paperboard

ABSTRACT

A high strength double-ply corrugated paperboard including upper (102) and lower (106) liners and multiple-ply corrugated mediums (101, 104) disposed between the liners (102, 106), thereby capable of exhibiting a high compressive strength while having a small thickness to minimize the packaging size, and effectively absorbing outside shock applied to the package to keep the packaged goods more safe.

TECHNICAL FIELD

The present invention relates in general to paperboards used forpackaging goods and, more particularly, to a high strength double-plycorrugated paperboard including upper and lower liners and multiple-plycorrugated mediums disposed between the liners, thereby capable ofexhibiting a high compressive strength while having a small thickness tominimize the packaging size, and effectively absorbing outside shockapplied to the package to keep the packaged goods more safe.

BACKGROUND ART

As well known to those skilled in the art, various fragile goods needingto be handled with care, for example expensive bottled cosmetics,electronic and electric products such as television sets, areconventionally packaged using rigid boxes with shock-absorbingmaterials. The above shock-absorbing materials are used for absorbingthe outside shock applied to the packaged goods and thereby protect thegoods from the shock.

In the prior art, both expanded polystyrene formed according to thecontours of the goods to be packaged and cardboard mounts folded intogiven shapes or partially cut out sufficient enough to hold the goods inthe package boxes are generally used as shock-absorbing materials. Whenthe goods to be packaged are heavy goods such as refrigerators, thepackaging materials for such goods need to be provided with bothexcellent shock absorption and rigidity sufficient enough to absorb theoutside shock and to bear the weight of the heavy goods. In order toachieve the above object, the package boxes for such heavy goods arepreferably bottomed with wooden pallets.

The expanded polystyrene used as a shock-absorbing material has anadvantage in that it is easily formed and suitable for mass production.However, the expanded polystyrene is breaks easily and induces staticelectricity. Therefore, the expanded polystyrene not only causesenvironmental contamination due to its broken pieces, but also isscarcely used for packaging precision goods due to the staticelectricity. Otherwise stated, use of the expanded polystyrene as theshock-absorbing material is limited as it remarkably reduces theexpected life of the packaged goods.

The cardboard mounts folded into given shapes or partially cut outsufficient enough to hold the goods in the package boxes are problematicin that they are not suitable for mass production. Furthermore, theabove cardboard mounts have inferior durability and generate paper dustwhile packaging the goods. Due to the inferior durability as well as thepaper dust, the above cardboard mounts may exert a bad influence uponthe expected life of the packaged goods.

In order to rectify the above problems, package cases formed using pulpmolds have been recently proposed and used. However, the above packagecases need to be formed using individual molds even when the cases areproduced on a small scale. As the molds should be produced by highlyskilled workers one by one, the package cases are problematic in that itis very difficult to produce the cases. Another problem of the abovepackage cases is resided in that they are expensive.

As people are recently becoming environmentally conscious, usedpackaging materials need appropriate treating to prevent them fromcausing environmental contamination. However, it has been noted thattreatment of various plastic packaging materials such as expandedpolystyrene is very difficult as the above plastic packaging materialscan not be recycled. The above plastic packaging materials will causeenvironmental contamination and exert a bad influence upon the ecosystemwhen they are simply discarded. Therefore, environmentally consciouspeople tend to avoid using such plastic packaging materials. Thus,demand for the above plastic packaging materials is reduced.

DISCLOSURE OF THE INVENTION

It is, therefore, an object of the present invention to provide a highstrength corrugated paperboard in which the above problems can beovercome and which has an improved structure suitable for not onlyreliably protecting the packaged goods, but also improving durability ofthe packaging paper sheet.

It is another object of the present invention to provide a double-plycorrugated paperboard having a value-added structure includingmultiple-ply corrugated mediums with different corrugation pitches andheights disposed between upper and lower liners, thereby capable ofexhibiting a high compressive strength while having a small thickness tominimize the packaging size.

It is a further object of the present invention to provide a cheap andregenerable corrugated paperboard which is not made of materials causingenvironmental contamination, but made of regenerable paper, and whichcan be produced through an automatic process.

In order to accomplish the above objects, the present invention providesa double-ply corrugated paperboard comprising: a liner having oppositesmooth surfaces; a first corrugated medium having continuouscorrugations with a predetermined corrugation pitch and a predeterminedcorrugation height, the first corrugated medium being laminated on onesurface of the liner, thereby forming a single-faced corrugatedpaperboard; and a second corrugated medium having continuouscorrugations with a predetermined corrugation pitch and a predeterminedcorrugation height, the second corrugated medium being laminated on thefirst corrugated medium of the single-faced corrugated paperboard,whereby the double-ply corrugated paperboard has an improvement in shockabsorptivity and an enhancement in the compressive strength against avertical load.

In accordance with an embodiment of the present invention, the first andsecond corrugated mediums have the same corrugation pitch, but havedifferent corrugation heights to define continuous shock absorbingspaces therebetween.

In accordance with another embodiment of the present invention, thefirst and second corrugated mediums have the same corrugation pitch andheight, but have different curvatures to define a pair of shockabsorbing spaces therebetween for every corrugation. Alternatively, thefirst and second corrugated mediums have different corrugation pitchessuch that the corrugation pitch of the second corrugated mediumcorresponds to two times the corrugation pitch of the first corrugatedmedium. The first and second corrugated mediums may also have the samecorrugation pitch and height such that they are completely in contactwith each other to construct a double-ply corrugated structure havingenhancements in compressive strength and stiffness. The double-plycorrugated paperboard may further comprise a pair of corrugated mediumsrespectively having the same constructions as the first and secondcorrugated mediums and laminated on the other surface of the liner. Thedouble-ply corrugated paperboard may further comprises at least onecorrugated medium laminated on the second corrugated medium.

The present invention also provides a method for producing a double-plycorrugated paperboard comprising the steps of: bonding, to a smoothliner, a first corrugated medium having continuous corrugations with apredetermined corrugation pitch and a predetermined corrugation height,and then pressing the first corrugated medium together with the liner bya press belt, thereby forming a single-faced corrugated paperboard;feeding the single-faced corrugated paperboard to a single-facedcorrugated paperboard forming station, and then laminating, on thesingle-faced corrugated paperboard, a second corrugated medium havingcontinuous corrugations with a predetermined corrugation pitch and apredetermined corrugation height such that corresponding corrugations ofthe first and second corrugated medium are overlapped with each other,thereby forming double-ply corrugated paperboard; guiding the double-plycorrugated paperboard to a paper guide, thereby controlling a feedingspeed of the double-ply corrugated paperboard; pre-heating thedouble-ply corrugated paperboard being continuously fed whilemaintaining the double-ply corrugated paperboard in a uniformly tensedstate; supplying a cover liner in parallel to the double-ply corrugatedpaperboard passing through the paper guide, along a path defined beneaththe double-ply corrugated paperboard; continuously coating an adhesiveon facing surfaces of the double-ply corrugated paperboard and coverliner; guide the adhesive-applied double-ply corrugated paperboard andcover liner along a heating plate; and pressing the double-plycorrugated paperboard and cover liner at a predetermined pressure duringthe double-ply corrugated paperboard and cover liner are fed along theheating plate, thereby bonding the double-ply corrugated paperboard andcover liner together.

The step of laminating the second corrugated medium on the single-facedcorrugated paperboard further comprises the steps of: sensing a positionof each corrugation on the single-faced corrugated paperboard; comparingthe sensed corrugation position with a position of each correspondingcorrugation of the second corrugated medium; and controlling a feedingspeed of the single-faced corrugated paperboard on the basis of theresult of the comparison.

The present invention also provides an apparatus for producing adouble-ply corrugated paperboard comprising: a medium supply roll and aliner supply roll respectively supplying a continuous, first medium anda continuous liner; first single-faced corrugated paperboard formingmeans adapted to receive the first medium and the liner respectivelyfrom the medium supply roll and the liner supply roll, to corrugate themedium and to bond the first, corrugated medium to the liner, therebyforming a single-faced corrugated paperboard; second single-facedcorrugated paperboard forming means adapted to receive the single-facedcorrugated paperboard from the first single-faced corrugated paperboardforming station and a continuous, second medium from another mediumsupply roll, to corrugate the second medium, to bond the corrugated,second medium to the single-faced corrugated paperboard, thereby forminga double-ply corrugated paperboard; a paper guide arranged downstreamthe second single-face corrugated paperboard forming means and adaptedto control a feeding speed of the double-ply corrugated paperboard; atension roll and pre-heating means both arranged downstream the paperguide and adapted to apply a constant tension to the double-plycorrugated paperboard being continuously fed; a cover liner supply rollarranged upstream the pre-heating means and adapted to supply acontinuous cover liner along a path parallel to the double-plycorrugated paperboard passing through the paper guide; adhesive coatingmeans adapted to continuously coat an adhesive on facing surfaces of thecover liner and second corrugated medium of the double-ply corrugatedpaperboard; and a heating plate and pressing belt means both adapted topress the adhesive-applied double-ply corrugated paperboard and coverliner at a predetermined pressure while heating them, thereby bondingthem together.

Each of the first and second single-faced corrugated paperboard formingmeans comprises: a pair of vertically arranged corrugator rollersadapted to guide the corresponding medium therebetween and to corrugatethe guided medium to have a desired wave; an adhesive coating rollerarranged on one side of the upper one of the corrugator rollers andadapted to uniformly coat an adhesive on one surface of the corrugatedmedium; and a laminating unit constituted by a press belt and a pair ofbelt driving rolls all disposed above the upper corrugator roller andadapted to bring the liner in the case of the first forming means or thesingle-faced corrugated paperboard in the case of the second formingmeans into contact with the corrugated medium passing over the uppercorrugator roller.

BRIEF DESCRIPTION OF DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a schematic view illustrating an apparatus for producing adouble-ply corrugated paperboard in accordance with the presentinvention;

FIG. 2 is a schematic view illustrating a single-faced corrugatedpaperboard forming station included in the apparatus of the presentinvention;

FIG. 3 is a schematic view illustrating a single-faced double-plypaperboard forming station included in the apparatus of the presentinvention; and

FIGS. 4A to 4E are sectional views respectively illustrating paperboardsproduced in accordance with a paperboard producing method of the presentinvention wherein

FIG. 4A shows a single-faced corrugated paperboard structure including asingle corrugated medium,

FIG. 4B shows a double-ply corrugated paperboard structure including apair of corrugated mediums with the same corrugation pitch, butdifferent corrugation heights,

FIG. 4C shows a double-ply corrugated paperboard structure including apair of corrugated mediums with the same corrugation pitch and height,but different curvatures,

FIG. 4D shows a double-ply corrugated paperboard structure including apair of corrugated mediums with different corrugation pitches, and

FIG. 4E shows a double-ply corrugated paperboard structure including apair of corrugated mediums with the same corrugation pitch and height tobe completely in contact with each other.

FIGS. 5A and 5B are enlarged sectional views respectively showing theconstruction of double-ply corrugated paperboards of this invention.

FIG. 5A is a sectional view showing the position of the bonded portionsformed between two corrugated mediums and the liners of the paperboardin accordance with an embodiment of this invention.

FIG. 5B is a sectional view of a high-elastic corrugated paperboardhaving bonded portions selectively formed on some of the contactportions between the corrugated mediums and the liners of the paperboardin accordance with another embodiment of this invention.

BEST MODE FOR CARRYING OUT THE INVENTION

FIGS. 1 to 3 illustrate an apparatus for producing a continuousdouble-ply corrugated paperboard in accordance with the presentinvention, respectively.

As shown in FIGS. 1, the apparatus for producing a continuous double-plycorrugated paperboard includes a first single-faced corrugatedpaperboard forming station 10 which receives a medium 101 and a liner102 from a medium supply roll 11 and a liner supply roll 12,respectively, and forms a single-faced corrugated paperboard 103.Although the construction of the first single-faced corrugatedpaperboard forming station 10 is not shown in FIG. 1 in detail, it canbe clearly understood by referring to FIG. 2 which shows a secondsingle-faced corrugated paperboard forming station 40 having the sameconstruction as the first single-faced corrugated paperboard formingstation 10. The first single-faced corrugated paperboard forming station10 includes a pair of corrugator rollers 13 and 14 adapted to guide themedium 101 therebetween and to corrugate the medium 101 to have adesired wave, an adhesive coating roller 15 arranged on one side of theupper corrugator roller 13 and adapted to uniformly coat an adhesive onone surface of the medium 101, and a laminating unit constituted by apress belt 10 and a pair of belt driving rolls 20 all disposed above theupper corrugator roller 13 and adapted to bring the liner 102 fed fromthe liner supply roll 12 into contact with the corrugated medium 101passing over the corrugator roller 13. Between the liner supply roll 12and the corrugator roller 13, a speed-adjustable accelerating roll 21 isarranged to adjust the speed of the liner 102 fed toward the corrugatorroller 13. Guide tension rolls 22 are also disposed between the mediumsupply roll 11 and the corrugator roller 13 or 14 to apply a desiredtension to the medium 101 fed toward the corrugator roller.

The corrugator rollers 13 and 14 are vertically arranged to engage witheach other such that a regular wave of the medium 101 is continuouslyformed. The upper corrugator roller 13 is provided at its outercorrugated surface with a plurality of suction holes (not shown)arranged along each groove of the roller 13. When the medium 101 to bebond to the liner 102 passes between the corrugator rollers 13 and 14,it is in close contact with the corrugated surface of the corrugatorroller 13 by a strong suction applied thereto through the suction holesso that it can maintain its desired wave shape. In other words, thesuction holes serve to maintain the corrugated shape of the medium 101,which is corrugated to have the desired wave while passing between thecorrugator rollers 13 and 14, without any damage until the corrugatedmedium 101 is bonded to the liner 102. The suction is continuouslyapplied to the medium 101 until the medium 101 reaches a position whereit comes into contact with the liner 102.

It is preferred that the corrugator rollers 13 and 14, which corrugatethe medium 101 fed from the medium supply roll 11 to have corrugationshaving a desired pitch and a desired height, are of a cartridge typeenabling a replacement thereof. In this case, it is possible tocontinuously produce a corrugated paperboard having various waves withdifferent corrugation heights and pitches as shown in FIGS. 4A to 4E bysimply replacing the corrugator rollers 13 and 14 by new ones withoutany replacement of the entire single-faced corrugated paperboard formingstation.

As shown in FIG. 2, the adhesive coating roller 15, which applies anadhesive to one surface of the corrugated medium 101 on one side of theupper corrugator roller 13, is preferred to be in contact with anadhesive transfer roller 17 which is dipped in an adhesive storage tank16 filled with the adhesive. As the adhesive coating roller 15 rotates,the adhesive on the adhesive transfer roller 17 is transferred to theadhesive coating roller 15. With such a construction, the adhesive canbe rapidly transferred to the corrugated medium 101.

Alternatively, another adhesive coating means may be used. For example,a nozzle-attached plate construction may be used which includes aplurality of nozzles aligned in a line with one another. In this case,selected one of the nozzles are opened depending on the shape of thecorrugated medium so that the width and space of adhesive coatings onthe corrugated medium can be optionally adjusted. In addition to theadhesive transfer roller 17, a separate dipping roller may be providedwhich is dipped in the adhesive storage tank 16. In this case, theadhesive transfer roller 17 is arranged between the dipping roller andthe adhesive coating roller 15 so that it can transfer the adhesive fromthe dipping roller 18 to the adhesive coating roller 15. In this case,it is possible to more uniformly apply the adhesive to the corrugatedmedium 101.

Upstream the first single-faced corrugated paperboard forming station10, a pre-heating unit 23 is arranged, as shown in FIG. 1. Thepre-heating unit 23 serves to pre-heat the liner 102 to a temperaturerequired for the bonding before the liner 102 is fed to the firstsingle-faced corrugated paperboard forming station 10. Downstream thefirst single-faced corrugated paperboard forming station 10, the secondsingle-faced corrugated paperboard forming station is arranged which isdenoted by the reference numeral 40 and has the same construction as thefirst single-faced corrugated paperboard forming station 10.

The second single-faced corrugated paperboard forming station 40 issupplied with the single-faced corrugated paperboard 103 emerging fromthe first single-faced corrugated paperboard forming station 10 in placeof the liner. The second single-faced corrugated paperboard formingstation 40 bonds another corrugated medium 104 fed from a medium supplyroll 41 to the single-faced corrugated paperboard 103. In this regard,the second single-faced corrugated paperboard forming station 40 has thesame construction as the first single-faced corrugated paperboardforming station 10 except that it receives the single-faced corrugatedpaperboard 103 in place of the liner. In other words, the secondsingle-faced corrugated paperboard forming station 40 does not requireany separate liner supply roll.

Similarly to the liner 102 guided to the first single-faced corrugatedpaperboard forming station 10, the single-faced corrugated paperboard103 guided to the second single-faced corrugated paperboard formingstation 40 passes over a pre-heating unit 44 so that it can bepre-heated to a temperature required for the bonding thereof.

Upstream the speed-adjustable accelerating roll 21 of the secondsingle-faced corrugated paperboard forming station 40, a suction brake42 is arranged to control the speed of the single-faced corrugatedpaperboard 103 fed to the upper corrugator roller 13 of the secondsingle-faced corrugated paperboard forming station 40.

The suction brake 42 is controlled by a corrugation position sensor 43disposed between the speed-adjustable accelerating roll 21 and the pressbelt 19 in the second single-faced corrugated paperboard forming station40.

In other words, the corrugation position sensor 43 senses positions ofcorrugations of the single-faced corrugated paperboard 103 between thespeed-adjustable accelerating roll 21 and the press belt 19 so that thecorrugation position of the single-faced corrugated paperboard 103 cancoincide with the corrugation position of the corrugated medium 104 atthe upper corrugator roller 13 of the second single-faced corrugatedpaperboard forming station 40.

A paper guide 25 is arranged at the exit of the second single-facedcorrugated paperboard forming station 40 in order to control the feedingspeed of a single-faced double-ply corrugated paperboard 105 with twocorrugated mediums 101 and 104 bonded thereto, as shown in FIGS. 1 and3.

By the provision of the paper guide 25, the single-faced double-plycorrugated paperboard 105 can be freely fed along a bridge 24 under auniformly tensed condition. Downstream the paper guide 25, a tensionroll 26 and pre-heating units 27 are installed.

The tension roll 26 and one pre-heating unit 27 serve to apply asufficient tension to the single-faced double-fly corrugated paperboard105 whereas the other pre-heating unit 27 serves to apply a sufficienttension to a liner 106 which will be bonded to the single-faceddouble-ply corrugated paperboard 105. Adhesive coating units 29 aredisposed downstream the pre-heating units 27 to apply an adhesive to theouter corrugated medium of the single-faced double-ply corrugatedpaperboard 105 and the liner 106, respectively. A heating plate 30 and apair of press belts 31 are arranged downstream the pre-heating units 27.The single-faced double-ply corrugated paperboard 105 and liner 106 bothapplied with the adhesive are fed through a gap defined between thepress belts 31 and pressed against each other by a uniform pressureprovided by the press belts 31 while being heated by the heating plate30. Thus, a double-ply corrugated paperboard having a good quality canbe produced.

Now, operation of the apparatus having the above-mentioned arrangementin accordance with the present invention will be described.

As the first single-faced corrugated paperboard forming station 10receives the first medium 101 and the first liner 102 respectively fromthe medium supply roll 11 and the liner supply roll 12, it corrugatesthe medium 101 to have a desired corrugation pitch and a desiredcorrugation height and then bonds the corrugated medium 101 to thesmooth liner 102 while pressing them by means of the press belt 19,thereby forming the single-faced corrugated paperboard 103.

Since the press belt 19 is constructed to surround a pair of beltdriving rolls 20 and to press the upper portion of the upper corrugatorroller 13 at its lower portion, it is possible to effectively preventany press roll mark from being formed on the single-faced corrugatedpaperboard 103 being produced.

The single-faced corrugated paperboard 103 emerging from the firstsingle-faced corrugated paperboard forming station 10 is fed to thesecond single-faced corrugated paperboard forming station 40 which, inturn, bonds the second medium 104, which has been corrugated, to thesingle-faced corrugated paperboard 103, thereby forming the single-faceddouble-ply corrugated paperboard 105 with the paperboard 103 and secondcorrugated medium 104 laminated together.

In the formation of this single-faced double-ply corrugated paperboard105, it is desirable to accurately control the speed of the corrugatorrollers and the speed-adjustable accelerating roll, thereby moreaccurately adjusting the corrugation pitch. This can be achieved bycorrecting a deviation generated between an AC servo motor (not shown)for driving the speed-adjustable accelerating roll and an AC servo motor(not shown) for driving the corrugator rollers. This deviationcorrection can be achieved by counting pitches of the servo motors bysensors, operating data generated by the sensors every counting time,deriving speed data from a phase difference based on the result of theoperation, and then transmitting the speed data to a servo amplifier forcontrolling one or two servo motors. Alternatively, the relative feedingspeeds of the single-faced corrugated paperboard and the second mediummay be controlled by continuously checking the cross-section of thesingle-faced corrugated paperboard at intervals of 1/1,000 to 1/10,000second by a super-high speed camera (image), transferring an instantcorrugation pitch error in the form of image data to a centralprocessing unit, deriving speed data from a phase difference based onthe instant corrugation pitch error, and then transmitting to a servoamplifier for controlling AC servo motors for the speed-adjustableaccelerating roll and corrugator rollers.

This single-faced double-ply corrugated paperboard 105 from the secondsingle-faced corrugated paperboard forming station 40 is guided to thepaper guide 25 which controls the feeding speed of the paperboard 105.After passing through the paper guide 25, the single-faced double-plycorrugated paperboard 105 passes over the tension roll 26 and thepre-heating unit 27 associated therewith. As a result, the paperboard105 is maintained at a tensed state while being pre-heated at itssurface to a desired temperature.

During the single-faced double-ply corrugated paperboard 105 is fedthrough the paper guide 25, the second liner 106 is fed in parallel tothe paperboard 105 beneath the feeding path of the paperboard 105. Boththe paperboard 105 and the second liner 106 are then fed to the nipbetween the press belts 31. Before the paperboard 105 and the secondliner 106 reach the press belts 31, they are coated with an adhesive. Asthe paperboard 105 and the second liner 106 pass through the nip betweenthe press belts 31, they are pressed against each other by the pressbelts 31 while being heated by the heating plate 30 disposed beneath thepress belts 31. Accordingly, the paperboard 105 and the second liner 106are firmly bonded together. Thus, a desired double-ply corrugatedpaperboard is produced.

For accurately laminating the second corrugated medium 104 on thesingle-faced corrugated paperboard 103 bonded with the corrugated medium101, it is required to accurately sense the position of each corrugationon the paperboard 103, compare the sensed corrugation position with theposition of each corresponding corrugation of the second corrugatedmedium 104 and thereby controlling the feeding speed of the single-facedcorrugated paperboard 103.

The double-ply corrugated paperboard produced through the aboveprocedures in accordance with the present invention can have variousshapes and constructions as shown in FIGS. 4B to 4E. This can beaccomplished by appropriately varying the dimensions of the corrugatorrollers 13 and 14 provided at the first and second single-facedcorrugated paperboard forming stations 10 and 40.

Of factors determining the dimensions of the corrugator rollers 13 and14 required for producing a desired double-ply corrugated paperboard,the most important one is the ratio between the corrugation pitch of thelower corrugations and the corrugation pitch of the upper corrugations.This corrugation pitch ratio determines the shock absorptivity anddurability of the final product, namely, the double-ply corrugatedpaperboard.

Where only the first single-faced corrugated paperboard forming station10 is driven while stopping the second single-faced corrugatedpaperboard forming station 40, a single-ply corrugated paperboard havinga conventional shape is produced which includes the single-facedcorrugated paperboard 103 with the corrugated medium 101 and the liner102, and the liner 106 laminated on the paperboard 103, as shown in FIG.4A. On the other hand, where both the first and second single-facedcorrugated paperboard forming stations 10 and 40 are driven whilevarying the dimensions of the corrugator rollers 13 and 14 thereof,various double-ply corrugated paperboards having different constructionscan be produced, as shown in FIGS. 4B to 4E.

Where a double-ply corrugated paperboard having upper and lowercorrugations with the same corrugation pitch, but with differentcorrugation heights is to be produced, as shown in FIG. 4B, it isrequired to use, for the first and second forming stations 10 and 40,two different sets of corrugator rollers 13 and 14 having a corrugationpitch ratio of 1:1, namely, the same corrugation pitch, but havingdifferent corrugation heights.

In this case, the double-ply corrugated paperboard has a space definedbetween facing upper and lower corrugations by virtue of differentcorrugation heights, as shown in FIG. 4B. When this double-plycorrugated paperboard is subjected to a shock from the outside, theshock is primarily absorbed by the space. For a higher shock, it issecondarily absorbed by the lower corrugated medium 101 of thedouble-ply corrugated paperboard. Thus, the shock absorption iseffectively achieved.

Where a double-ply corrugated paperboard having upper and lowercorrugations with the same corrugation pitch and the same corrugationheight is to be produced, as shown in FIG. 4C, two identical sets ofcorrugator rollers 13 and 14 having the same corrugation pitch and thesame corrugation height are used for the first and second formingstations 10 and 40, respectively. In this case, however, it is requiredto form corrugations constituted by alternating crests and valleys bothhaving different curvatures at their peaks from each other so that theupper and lower corrugations have spaces defined between each valley andeach crest overlapping with the valley. Here, the valleys arecorrugation portions bonded to the corresponding liner at their peaks.In this case, a variety of shock absorption effects can be expected byvarying the corrugation shape and the corrugation height.

Where a double-ply corrugated paperboard in which its upper corrugationshave a corrugation pitch corresponding to 2 times that of its lowercorrugations is to be produced, as shown in FIG. 4D, it is required touse, for the first and second forming stations 10 and 40, two differentsets of corrugator rollers 13 and 14 having a corrugation pitch ratio of2:1.

In this case, each valley of the lower corrugated medium 104 having alarger corrugation pitch overlaps with two successive crests of theupper corrugated medium 101 having a smaller corrugation pitch. Whenthis double-ply corrugated paperboard is subjected to a load from theoutside, each valley of the lower corrugations is pushed toward thevalley defined between the corresponding crests of the uppercorrugations. Simultaneously, the crests of the upper corrugations arepushed into the corresponding valley of the lower corrugations. When theload is released before the elastic limit of the upper and lowercorrugated mediums 101 and 104, the strain is completely removed so thatthe corrugated mediums 101 and 104 can return to their original states,respectively. In this case, accordingly, the double-ply corrugatedpaperboard can have a durable shock absorptivity.

On the other hand, in a case of a double-ply corrugated paperboard inwhich its upper and lower corrugated mediums 101 and 104 are completelyin contact with each other, as shown in FIG. 4E, it achieves animprovement in the compressive strength against an axial load and anincrease in bending stiffness as well as a shock absorption effect.

In addition, it is preferable to form a double-ply corrugated paperboardin which the upper and lower corrugated mediums 101 and 104 arecompletely overlapped with respect to each other and are bonded to lines102 and 106 at their crests and valleys but are not bonded togetherexcept for the portions corresponding to the crests and valleys.

In other words, when the two corrugated mediums 101 and 104 arecompletely bonded together in the junction between them, the strength ofthe resulting corrugated paperboard is increased dramatically. However,such a corrugated paperboard cannot effectively absorb external shockbut regrettably transmits the shock to the packaged material thussometimes causing the packaged material to break. In this regard, theuse of the paperboard has to be limited to the packaging of a materialhaving a high shock resistance.

Therefore, it is required to provide a corrugated paperboard which has adesirable compressive strength and quickly absorbs external shock thuspreventing a packaged material from breaking. In order to achieve theabove object, two corrugated mediums 101 and 104 are arranged to beoverlapped with each other as shown in FIG. 5A, thus increasing theresistance against a vertical load. The two corrugated mediums 101 and104 are bonded to liners 102 and 106 at their crests and valleys but arenot bonded together except for the portions corresponding to the crestsand valleys, so that the mediums 101 and 104 are allowed to beindividually deformed as shown in the dotted line of FIG. 5A when anexternal shock is applied to the paperboard.

FIG. 5B shows a corrugated paperboard in accordance with anotherembodiment of the invention. The above corrugated paperboard iseffectively used for packaging a material that is hypersensitive ofshock. The corrugated paperboard shown in FIG. 5B is produced by bondingsome of the crests and valleys of the corrugated mediums 101 and 104 tolines 102 and 106 thus intermittently and repeatedly forming bondedportions 202 in the junctions between the mediums and liners whileproducing the paperboards of FIGS. 4B to 4E.

In this case, it is preferable to form the bonded portions 202 with atleast two nonbonded and movable crests or valleys of a medium remainingbetween neighboring bonded portions 202.

In the above corrugated paperboard, the nonbonded crests and valleys ofthe mediums 101 and 104 may freely move relative to liners 102 and 106within the range defined between the bonded portions 202 a shown in thedotted line of FIG. 5B. Since the nonbonded crests and valleys of themediums 101 and 104 can move as described above, it is possible tovariously change the distribution of the crests or valleys in a unitarea thus freely designing the construction of the corrugated paperboardin accordance with characteristics of materials to be packaged. Such aconstruction of the corrugated mediums 101 and 104 effectively supportsa movement of a packaged material in cooperation with the intrinsicdurability of liner 102. The above corrugated paperboard is thuseffectively used for packaging a material that is easily movable in thepackage.

It is also possible to laminate a plurality of single-faced double-plycorrugated paperboards having various constructions as above-mentionedin a manner that the corrugations of all the corrugated paperboards facein the same direction or in a manner that the corrugations of adjacentpaperboards face in opposite directions. In either case, a variety ofshock absorption effects can be expected by virtue of the differences incorrugation shape and corrugation height between adjacent laminatedpaperboards.

As apparent from the above description, the double-ply corrugatedpaperboard according to the present invention includes a plurality ofcorrugated mediums laminated together such that adjacent ones of thecorrugated mediums are completely in contact with each other orpartially in contact with each other at intervals. In such a laminatedstructure, even when one of two facing corrugated mediums is damaged dueto a shock from the outside, the elasticity and shock absorptivity ofthe paperboard is still maintained by the other corrugated medium.Moreover, the double-ply corrugated paperboard of the present inventionhave an internal shock absorptivity provided by its paper material aswell as a durability and a stiffness both provided by the wave of itscorrugated medium. In terms of the weight, the paperboard of the presentinvention is considerably light, as compared to conventional wood orsynthetic resin pallets. In this regard, the present paperboard has aconvenience in use. There is also an advantage that no accident occursdue to a carelessness in handling.

Although the preferred embodiments of the invention have been disclosedfor illustrative purposes, those skilled in the art will appreciate thatvarious modifications, additions and substitutions are possible, withoutdeparting from the scope and spirit of the invention as disclosed in theaccompanying claims.

Industrial Applicability

As apparent from the above description, the present invention provides adouble-ply corrugated paperboard produced by bonding, to a smooth liner,a first corrugated medium having continuous corrugations with a desiredcorrugation pitch and a desired corrugation height, thereby forming asingle-faced corrugated paperboard, and then laminating, on thesingle-faced corrugated paperboard, a second corrugated medium havingcontinuous corrugations with a desired corrugation pitch and a desiredcorrugation height. With such a structure, the double-ply corrugatedpaperboard of the present invention exhibits an improvement in shockabsorptivity and an enhancement in the compressive strength against avertical load. In accordance with the present invention, the paperboardis entirely made of regenerable paper other than materials causing anenvironmental contamination. In accordance with the present invention, aplurality of corrugated mediums may be laminated together between upperand lower liners of the paperboard such that adjacent ones of thecorrugated mediums are completely in contact with each other orpartially in contact with each other at intervals. Accordingly, it ispossible to increase the compressive strength of the paperboard and yetmaintain a small thickness of the paperboard. By virtue of thisadvantage, it is possible to provide high value-added paperboardscapable of effectively achieving a minimized packaging size. Once thepaperboard of the present invention is used for its packaging purpose,it may be reused as shock absorbing materials for packaging after it iscollected. In this regard, the present paperboard is a high value-addedproduct. Therefore, the present invention can greatly reduces theexpense of the packaging material and contributes to the protection ofenvironment and the reuse of the resource. Since the present paperboardcan effectively absorb a shock applied from the outside to a packagedcontent, it can keep the packaged content more safe.

We claim:
 1. A double-ply corrugated paperboard comprising:a firstliner; a first corrugated medium continuously and automaticallylaminated onto a surface of the first liner to form a single-facedsingle-ply corrugated paperboard, said first corrugated medium havingpredetermined flute pitch and flute peak height, the first corrugatedmedium is spot-bonded to the liner by applying a bonding agent onjunctions between crests of the first corrugated medium and the firstliner; a second corrugated medium continuously and automaticallylaminated onto the first corrugated medium of the single-facedsingle-ply corrugated paperboard to form a single-faced double-plycorrugated paperboard, said second corrugated medium having selectedflute pitch and flute peak height which are either the same as ordifferent from the flute pitch and flute peak height of the firstcorrugated medium, respectively, the second corrugated medium beingspot-bonded to the first corrugated medium on junctions between crestsof the second corrugated medium and crests of the first corrugatedmedium; and a second liner continuously and automatically laminated ontothe second corrugated medium of said single-faced double-ply corrugatedpaperboard to form a double-faced double-ply corrugated paperboard, thesecond corrugated medium being spot-bonded to the second liner onjunctions between valleys of the second corrugated medium and the secondliner.
 2. A double-ply corrugated paperboard comprising:a first liner; afirst corrugated medium continuously and automatically laminated onto asurface of the first liner to form a single-faced single-ply corrugatedpaperboard, said first corrugated medium having predetermined flutepitch and flute peak height; a second corrugated medium continuously andautomatically laminated onto said single-faced double-ply corrugatedpaperboard, said second corrugated medium having selected flute pitchand flute peak height which are either the same as or different from theflute pitch and flute peak height of the first corrugated medium,respectively, wherein the first and second corrugated mediums have thesame corrugation pitch, but have different corrugation heights to definecontinuous shock absorbing spaces therebetween; and a second linercontinuously and automatically laminated onto said single-faceddouble-ply corrugated paperboard to form a double-faced double-plycorrugated paperboard.
 3. A double-ply corrugated paperboardcomprising:a first liner; a first corrugated medium continuously andautomatically laminated onto a surface of the first liner to form asingle-faced single-ply corrugated paperboard, said first corrugatedmedium having predetermined flute pitch and flute peak height; a secondcorrugated medium continuously and automatically laminated onto saidsingle-faced double-ply corrugated paperboard, said second corrugatedmedium having selected flute pitch and flute peak height which areeither the same as or different from the flute pitch and flute peakheight of the first corrugated medium, respectively, wherein the firstand second corrugated mediums have the same corrugation pitch andheight, but have different curvatures to define a pair of shockabsorbing spaces therebetween for every corrugation; and a second linercontinuously and automatically laminated onto said single-faceddouble-ply corrugated paperboard to form a double-faced double-plycorrugated paperboard.
 4. A double-ply corrugated paperboardcomprising:a first liner; a first corrugated medium continuously andautomatically laminated onto a surface of the first liner to form asingle-faced single-ply corrugated paperboard, said first corrugatedmedium having predetermined flute pitch and flute peak height; a secondcorrugated medium continuously and automatically laminated onto saidsingle-faced double-ply corrugated paperboard, said second corrugatedmedium having selected flute pitch and flute peak height which areeither the same as or different from the flute pitch and flute peakheight of the first corrugated medium, respectively, wherein the firstand second corrugated mediums have different corrugation pitches suchthat the corrugation pitch of the second corrugated medium correspondsto two times the corrugation pitch of the first corrugated medium; and asecond liner continuously and automatically laminated onto saidsingle-faced double-ply corrugated paperboard to form a double-faceddouble-ply corrugated paperboard.
 5. The double-ply corrugatedpaperboard in accordance with claim 1, wherein the first and secondcorrugated medium have the same corrugation pitch and height such thatthey are completely in contact with each other, the second corrugatedmedium further being spot-bonded to the first corrugated medium onjunctions between valleys of the second corrugated medium and valleys ofthe first corrugated medium.
 6. A double-ply corrugated paperboardcomprising:a first liner; a first corrugated medium continuously andautomatically laminated onto a surface of the first liner to form asingle-faced single-ply corrugated paperboard, said first corrugatedmedium having predetermined flute pitch and flute peak height; a secondcorrugated medium continuously and automatically laminated onto saidsingle-faced double-ply corrugated paperboard, said second corrugatedmedium having selected flute pitch and flute peak height which areeither the same as or different from the flute pitch and flute peakheight of the first corrugated medium, respectively; a second linercontinuously and automatically laminated onto said single-faceddouble-ply corrugated paperboard to form a double-faced double-plycorrugated paperboard; and a pair of corrugated mediums respectivelyhaving the same constructions as the first and second corrugated mediumsand laminated on the other surface of the first liner.
 7. The double-plycorrugated paperboard in accordance with claim 6, further comprising atleast one corrugated medium laminated on the second corrugated medium.8. A method for producing a double-ply corrugated paperboard comprisingthe steps of:providing a first liner to a single-faced single-plycorrugated paperboard forming station; bonding a first corrugated mediumonto the first liner, said first corrugated medium having predeterminedflute pitch and flute peak height; pressing the first corrugated mediumand the first liner by a press belt to form a single-faced single-plycorrugated paperboard; feeding the single-faced single-ply corrugatedpaperboard to a single-faced double-ply corrugated paperboard formingstation; laminating a second corrugated medium onto the single-facedsingle-ply corrugated paperboard to form a single-faced double-plycorrugated paperboard, said second corrugated medium having selectedflute pitch and flute peak height which are the same as or differentfrom the flute pitch and flute peak height of the first corrugatedmedium, respectively; guiding the single-faced double-ply corrugatedpaperboard to a paper guide a feeding speed of the single-faceddouble-ply corrugated paperboard; pre-heating the single-faceddouble-ply corrugated paperboard in a uniformly tensed state; supplyinga second liner in parallel relationship to the single-faced double-plycorrugated paperboard which passes through the paper guide; coatingadhesive onto the single-faced double-ply corrugated paperboard and/orthe second liner; guiding the adhesive-applied single-faced double-plycorrugated paperboard and the second liner along a heating plate; andpressing the single-faced double-ply corrugated paperboard and thesecond liner while the single-faced double-ply corrugated paperboard andthe second liner are fed along the heating plate to thereby bond thesingle-faced double-ply corrugated paperboard and the second linertogether.
 9. The method in accordance with claim 8, wherein the step oflaminating the second corrugated medium on the single-faced corrugatedpaperboard further comprises the steps of:sensing a position of eachcorrugation on the single-faced corrugated paperboard; comparing thesensed corrugation position with a position of each correspondingcorrugation of the second corrugated medium; and controlling a feedingspeed of the single-faced corrugated paperboard on the basis of theresult of the comparison.
 10. The method in accordance with claim 8,wherein the step of laminating the second corrugated medium on thesingle-faced corrugated paperboard further comprises the step ofcorrecting a deviation generated between an AC servo motor for driving aspeed-adjustable accelerating roll used to adjust a feeding speed of thesingle-faced corrugated paperboard and an AC servo motor for drivingcorrugator rollers used to corrugate and feed the second medium, thedeviation correction being achieved by counting pitches of the servomotors by sensors, operating data generated by the sensors everycounting time, deriving speed data from a phase difference based on theresult of the operation, and then transmitting the speed data to a servoamplifier for controlling one or two servo motors.
 11. The method inaccordance with claim 8, wherein the step of laminating the secondcorrugated medium on the single-faced corrugated paperboard furthercomprises the steps of:continuously checking the cross-section of thesingle-faced corrugated paperboard at intervals of 1/1,000 to 1/10,000second by a super-high speed camera; transferring an instant corrugationpitch error in the form of image data to a central processing unit;deriving speed data from a phase difference based on the instantcorrugation pitch error; and transmitting the speed data to a servoamplifier for controlling an AC servo motor for driving aspeed-adjustable accelerating roll used to adjust a feeding speed of thesingle-faced corrugated paperboard or an AC servo motor for drivingcorrugator rollers used to corrugate and feed the second medium.
 12. Anapparatus for producing a double-ply corrugated paperboard comprising:afirst liner supply roll for continuously supplying a first liner; afirst medium supply roll for continuously supplying a first medium;single-faced single-ply corrugated paperboard forming means adapted forreceiving the first liner and the first medium from the first linersupply roll and the first medium supply roll, respectively, to corrugatethe first medium and then bond the corrugated first medium onto thefirst liner thereby to form a single-faced single-ply corrugatedpaperboard; a second medium supply roll for continuously supplying asecond medium; single-faced double-ply corrugated paperboard formingmeans adapted for receiving the single-faced single-ply corrugatedpaperboard and the second medium from the single-faced single-plycorrugated paperboard forming station and the second medium supply roll,respectively, to corrugate the second medium and then bond thecorrugated second medium to the single-faced single-ply corrugatedpaperboard thereby to form a single-faced double-ply corrugatedpaperboard; a paper guide arranged downstream the single-faceddouble-ply corrugated paperboard forming means for controlling a feedingspeed of the single-faced double-ply corrugated paperboard; a tensionroll and pre-heating means both arranged downstream the paper guide andadapted to apply a tension to the single-faced double-ply corrugatedpaperboard; a second liner supply roll arranged upstream the pre-heatingmeans for supplying a second liner along a path parallel to thesingle-faced double-ply corrugated paperboard passing through the paperguide; adhesive coating means adapted for coating adhesive onto thesecond corrugated medium of the single-faced double-ply corrugatedpaperboard and/or the second liner; and a heating plate and a pressingbelt for pressing the adhesive-applied single-faced double-plycorrugated paperboard and the second liner while heating them therebybonding them together.
 13. The apparatus in accordance with claim 12,wherein each of the first and second single-faced corrugated paperboardforming means comprises:a pair of vertically arranged corrugator rollersadapted to guide the corresponding medium therebetween and to corrugatethe guided medium to have a desired wave; an adhesive coating rollerarranged on one side of the upper one of the corrugator rollers andadapted to uniformly coat an adhesive on one surface of the corrugatedmedium; and a laminating unit constituted by a press belt and a pair ofbelt driving rolls all disposed above the upper corrugator roller andadapted to bring the liner in the case of the first forming means or thesingle-faced corrugated paperboard in the case of the second formingmeans into contact with the corrugated medium passing over the uppercorrugator roller.
 14. The apparatus in accordance with claim 13,wherein the corrugator rollers are vertically arranged to engage witheach other such that a regular wave of the corresponding medium iscontinuously formed, and the upper corrugator roller is provided at anouter corrugated surface thereof with a plurality of suction holesarranged along each groove thereof, the suction holes serving tomaintain the corrugated shape of the corrugated medium until thecorrugated medium is bonded to the liner in the case of the firstforming means or to the single-faced corrugated paperboard in the caseof the second forming means.
 15. The apparatus in accordance with claim14, wherein the corrugator rollers are of a cartridge type enabling areplacement thereof.
 16. The apparatus in accordance with claim 12,further comprising:a pair of speed-adjustable accelerating rollsrespectively arranged upstream the first and second single-facedcorrugated paperboard forming means, the speed-adjustable acceleratingrolls serving to adjust a feeding speed of the liner and a feeding speedof the single-faced corrugated paperboard, respectively; and a pair ofguide tension rolls respectively arranged upstream the first and secondsingle-faced corrugated paperboard forming means, the guide tensionrolls serving to apply a desired tension to the first and secondmediums, respectively.
 17. The apparatus in accordance with claim 16,further comprising a pair of suction brakes respectively arrangedupstream the speed-adjustable accelerating rolls, the suction brakesserving to control the feeding speed of the liner and the feeding speedof the single-faced corrugated paperboard, respectively.
 18. Theapparatus in accordance with claim 17, wherein the suction brake forcontrolling the feeding speed of the single-faced corrugated paperboardis controlled by a corrugation position sensor disposed beneath thespeed-adjustable accelerating roll arranged upstream the secondsingle-faced corrugated paperboard forming means, the corrugationposition sensor adapted to count positions of corrugations.
 19. Theapparatus in accordance with claim 12 further comprising a pair ofpre-heating means respectively arranged upstream the first and secondsingle-faced corrugated paperboard forming means, the pre-heating meansserving to pre-heat the liner and the single-faced corrugated paperboardto a temperature required for their bonding, respectively.
 20. Thedouble-ply corrugated paperboard in accordance with claim 1, whereinsaid spot-bonded portions are intermittently formed on the junctionbetween the valleys of the first corrugated medium and the liner thusallowing the first and second corrugated mediums to move relative to theliner within a range defined between the spot-bonded portions.
 21. Thedouble-ply corrugated paperboard in accordance with claim 20, whereinthe spot-bonded portions are formed on the junction between the valleysof the first corrugated medium and the liner with at least two nonbondedvalleys of the first corrugated medium remaining between neighboringbonded portions.